Sorry to disappoint, but, SA OHS&W Regulations, 1995. states in:
Division 2.13—Prevention of falls
2.13.1—Prevention of falls
(1) The purpose of this regulation is—
(a) to guard against falls that cause injuries due to the distances fallen; and
(b) to guard against persons falling into enclosures or containers that contain a
source of danger; and
(c) to ensure safe access to elevated workplaces; and
(d) to prescribe standards that must be observed in relation to the construction,
maintenance and use of ladders; and
(e) to prescribe standards that must be observed in relation to the performance of
maintenance work carried out above ground level on permanent structures.
(2) If—
(a) a person must work—
(i) in an elevated workplace from which he or she could fall; or
(ii) in the vicinity of an opening through which he or she could fall; or
(iii) in any other place from which he or she could fall,
and it is reasonably foreseeable that the person would be injured in such a fall
due to the distance of the fall; or(b) a person must work in the vicinity of an enclosure or container into which he
or she could fall and there is a reasonable likelihood that the person would be
injured in such a fall,
reasonable protection against a fall must be provided—
(c) by the provision of a safe means of access to the workplace; and
(d) by the provision of secure fences, covers or other forms of safeguarding or, if
that is not reasonably practicable due to the nature of the work, by the
provision and maintenance of safe systems of work.(3) If a person at work must gain access to a place that cannot be reached conveniently
from floor or ground level, and no appropriate means of mechanical access or fixed
stairway is available, a suitable ladder or steps must be provided.
(4) Any safeguarding provided for the purposes of subregulation (2)(d) must be kept in
good condition and must not be removed except so far as may be necessary to allow
the access or egress of any person or the shifting of materials.
(5) In determining the appropriate system of work for the purposes of
subregulation (2)(d), consideration must be given to—
(a) if a safe working platform cannot reasonably be provided, the use of a safety
harness attached to a secure structural
support (either directly or if that is not reasonably practicable, through the use
of an adequate static-line system);
(b) the use of a fall-arresting device (where appropriate);
(c) the undertaking of training in relation to the hazards that may be encounteredin the performance of the work;
(d) the provision of supervision by a competent person;
(e) the provision of assistance by another person.
As you can see from this regulation, even though no stated height is given, from the results of a risk assessment, if it is found that an injury is likely should a fall occur, then protection needs to be provided to prevent a fall from occurring.
My advice, purchase a roof workers kit and do some "safe working at heights training" I found it very usefull.